Add new royale ruleset.

royale.go

@@ -0,0 +1,82 @@
+package rules
+
+import (
+	"errors"
+)
+
+type RoyaleRuleset struct {
+	StandardRuleset
+
+	Turn              int32
+	ShrinkEveryNTurns int32
+
+	// Output
+	OutOfBounds []Point
+}
+
+func (r *RoyaleRuleset) CreateNextBoardState(prevState *BoardState, moves []SnakeMove) (*BoardState, error) {
+	if r.ShrinkEveryNTurns < 1 {
+		return nil, errors.New("royale game must shrink at least every 1 turn")
+	}
+
+	nextBoardState, err := r.StandardRuleset.CreateNextBoardState(prevState, moves)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: LOG?
+	err = r.populateOutOfBounds(nextBoardState)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: LOG?
+	err = r.eliminateOutOfBounds(nextBoardState)
+	if err != nil {
+		return nil, err
+	}
+
+	return nextBoardState, nil
+}
+
+func (r *RoyaleRuleset) populateOutOfBounds(b *BoardState) error {
+	r.OutOfBounds = []Point{}
+
+	if r.ShrinkEveryNTurns < 1 {
+		return errors.New("royale game must shrink at least every 1 turn")
+	}
+
+	if r.Turn < r.ShrinkEveryNTurns {
+		return nil
+	}
+
+	numShrinks := r.Turn / r.ShrinkEveryNTurns
+	minX, maxX := numShrinks, b.Width-1-numShrinks
+	minY, maxY := numShrinks, b.Height-1-numShrinks
+	for x := int32(0); x < b.Width; x++ {
+		for y := int32(0); y < b.Height; y++ {
+			if x < minX || x > maxX || y < minY || y > maxY {
+				r.OutOfBounds = append(r.OutOfBounds, Point{x, y})
+			}
+		}
+	}
+
+	return nil
+}
+
+func (r *RoyaleRuleset) eliminateOutOfBounds(b *BoardState) error {
+	for i := 0; i < len(b.Snakes); i++ {
+		snake := &b.Snakes[i]
+		if snake.EliminatedCause == NotEliminated {
+			head := snake.Body[0]
+			for _, p := range r.OutOfBounds {
+				if head == p {
+					// Snake is now out of bounds, eliminate it
+					snake.EliminatedCause = EliminatedByOutOfBounds
+				}
+			}
+		}
+	}
+
+	return nil
+}